Double impeller wheel

ABSTRACT

A double impeller wheel for axial flow fans comprising a set of inner impeller blades surrounded by an intermediate ring, a set of outer impeller blades secured to the ring, the width of the ring in an axial direction being less than that of the impeller blades.

United States Patent Kristiansen 1 Jan. 18, 972

[54] DOUBLE IMPELLER WHEEL 2,007,408 7/1935 Schellens ..4l5/79 2,790,5964/1957 Stirling ..4l5/77 X 1 lnvemorr Svend Belle Kristi-men, Naestvcd,3,186,166 6/1965 Grieb ..415/79 Ux Denmark FOREIGN PATENTS ORAPPLICATIONS [73] Assignee: Nordisk Ventilator Co. A/S, Naestved,

D k 60,579 4/ 1954 France ..4l6/242 327,058 41919 G ..4l6 193 [22 Filed:Mar. 13, 1970 I I 2 1 19,1 2 Primary Examiner-Everette A. Powell,Jr.

Attorney-Sughrue, Rothwell, Mion, Zinn & Macpeak [30] ForeignApplication Priority Data 7 A T C Mar. 3 l, 1969 Denmark 1790/69 Adouble impeller wheel f axial fl f comprising a set f inner impellerblades surrounded by an intermediate ring, a [52] Cl "416/193, 415/77set of outer impeller blades secured to the ring, the width of [51] Int.Cl ..F04d 19/00 the ring in an axial direction being less than that fthe [58] Field of Search ..4l6/193, 203, 210, 194, 196; pellet blades.

8 Claims, 6 Drawing Figures [56] References Cited UNITED STATES PATENTSLudeman ..415/79 DOUBLE IMPELLEIR WHEEL BACKGROUND OF THE INVENTION 1.Field of the Invention The present invention relates to a doubleimpeller wheel for axial flow fans with a set of inner impeller bladessecured to a hub, an intermediate ring mounted around the extremities ofthese blades and a set of outer impeller blades mounted on thisintermediate ring coaxially with the first set of outer impeller blades,and in which the two sets of blades are adapted to blow in oppositedirections.

2. Description of the Prior Art Such double impeller wheels are used,for instance, for the ventilation of rooms in buildings such as stables,in thatthey are mounted in two coaxial ducts with the inner bladestogether with the drive motor of the wheel in the innermost duct, andthe outer blades in the outermost annular duct. Since the two sets ofblades blow in opposite directions, it is thus possible for theextraction of air from the room through the one duct, and the injectionof fresh air through the second duct to take place.

On the spot, where the impeller wheel is mounted, there must of coursebe a break in the partition between the two coaxial ducts.

In the two ducts, there is going to be a, taking it by and large,constant different in the pressure, but with opposite signs on the twosides of the impeller wheel. The change in sign takes place essentiallyacross the width of the blades seen in the axial direction, and as thewidth of the intermediate ring usually corresponds to this blade width,it means that a significant difference in pressure exists between thetwo ducts on the spot where the edges of the partition between themfaces the intermediate ring. Since there must be a certain gap betweenthe edges of the partition and the intermediate ring, this difference inpressure gives rise to an air flow from the one duct to the other, sothat a certain loss occurs. At the same time, an annoying deposition ofdust takes place on the inside of the intermediate ring which, in thecourse of time, may reduce the efficiency and, moreover, may given riseto an imbalance.

SUMMARY OF THE INVENTION According to the present invention, thesedisadvantages are obviated by the axial width of the intermediate ringbeing considerably smaller than the width of the blades measured in theaxial direction from front edge to rear edge in the proximity of thepoints of the inner blades.

No difficulty is encountered in producing the intermediate ring having awidth which is considerably smaller than the width of the blades, sinceit is only necessary to see to it that the cross section remains of asufficient size in order to provide the necessary strength and that theconnection between the blades and the intermediate ring remainssufficiently strong.

Owing to the narrow intermediate ring, the gaps between the partitionand the ring are moved into an area where the difference in pressure isconsiderably smaller, so that the air flow between the two ducts is verysignificantly reduced.

According to the invention it is advantageous for the intermediate ringto be constructed with lateral surfaces of considerable width at rightangles to the axis of the wheel, as it is possible thereby to reduce therequirements as to tolerance in the manufacture of the partition betweenthe two ducts very considerably.

Furthermore, it is expedient according to the invention for the insideof the intermediate ring to be composed of surfaces sloping inwardstowards the center as thereby the risk of dust deposition is reducedstill further.

Finally, it may, according to the invention, be advantageous for thesection of the blades in the proximity of their securing surfaces on theintermediate ring to be turned in such a way that the securing surfacesof the blades extend in a direction which, at the most, will form asmall angle with a plane at right angles to the axis of the impellerwheel, by means of which a very strong securing of the blades even on avery narrow intermediate ring is made possible.

BRIEF DESCRIPTION OF THE DRAWINGS In the following, the invention isexplained in greater detail with reference to the drawing, in which FIG.1 shows diagrammatically a part of a known double impeller wheel mountedin coaxial ducts,

FIG. 2 shows a diagrammatical illustration of a double impeller wheelaccording to the invention shown in the same way as the wheel in FIG. 1,

FIG. 3 shows a pressure diagram for explaining the effect of theinvention,

FIG. 4 shows a part of an impeller wheel according to the invention on alarger scale in a special embodiment, and

FIG. 5 shows another part of an impeller wheel according to theinvention.

FIG. 6 shows the wheel as seen in an axial direction.

DESCRIPTION OF THE PREFERRED EMBODIMENT 5 FIG. 1 shows a motor 1, on theshaft of which a hub 2 is secured which carries a set of inner blades 3.Around the extremities of these blades, an intermediate ring 4 ismounted, which carries a set of outer blades 5. The motor 5 with theblade sets 3 and 5 is mounted in two coaxial ducts, of which the outerwall of the outermost duct 6 is denoted with 7, while the outer wall ofthe innermost duct 8, which, at the same time, forms the partitionbetween the two ducts, is denoted with 9. The intermediate ring 4 iscylindrical and of the same radius as the partition 9 and fills in abreak in same, the manufacturing tolerances rendering it necessarythough that on each side of the intermediate ring 4 there appears a gap10 and 1 l.

FIG. 1 represents the known construction of a double impeller wheel,while a double impeller wheel constructed according to the invention isshown diagrammatically in a corresponding manner in FIG. 2, in which thesame designations are employed for the individual parts.

The difference between the constructions shown in FIGS. 1 and 2 lies inthe fact that the intermediate ring 4 in FIG. 1, measured in the axialdirection, is of a width that corresponds to the width of the outerblades in theproximity of the blade base or the width of the innerblades measured in the proximity of the points of the blades, while thewidth of the intermediate ring 4 in FIG. 2 according to the invention isconsiderably less and, as is seen, only constitutes a fraction of thiswidth.

The effect of this difference is going to be explained in greater detailby means of the curves shown in FIG. 3.

In this figure, the curve I denotes the pressure condition in the duct6, while the curve II denotes the pressure condition in duct 8.

The two curves lie in the figure symmetrically with respect to the zeroline, but this will not always be the case, as the pressures in the twoducts, depending on the construction of the blade set, may possessdifferent numerical values.

The curves in FIG. 3 apply both to the known construction shown in FIG.1, as well as to the construction according to the invention shown inFIG. 2, provided that all dimensions in the two figures are identicalapart from the dimensions of the intermediate ring and the location ofthe gaps l0 and 11.

It is seen that the pressures in the ducts change signs in a point 0which approximately lies in a rnidplane through the blades at rightangles to the axis, in that FIGS. 1, 2 and 3 are drawn in such a way inrelation to each other that the abscissae from FIG. 3 can be directlytransferred to FIGS. I and 2.

It is seen, furthermore, that the pressure in the ducts remains constanton both sides of the impeller wheel all the way to the two lines markedA and B in FIG. 3. From these spots the pressures decrease practicallylinearly towards 0.

It follows herefrom that the difference in pressure between the twoducts 6 and 8, taking it by and large, are constant outside of bladesand here are of a very considerable magnitude, viz corresponding to thetotal of the numerical values of those pressures which are produced bythe two sets of blades.

It is seen that the gaps l and 11 in FIG. 1 are in two places whichcorrespond to the lines A and B in FIG. 3, that is to say, in placeswhere, to all intents and purposes, the maximum difference in pressurebetween the ducts exists. On the other hand, the gaps l0 and 11 in FIG.2 have been moved considerably closer together and are on a place whichin FIG. 2 is marked with lines C and D, i.e., on a place where thedifference in pressure between the two ducts has come very close to 0.

Since theoretically it can be anticipated that the gaps in the two casescan be made equally narrow, this means that the airflow from the oneduct to the other through these gaps is considerably less with theimpeller wheel according to the invention as shown in FIG. 2 than withthe known impeller wheel as shown in FIG. 1.

It appears from FIG. 4 that the intermediate ring 4 in this embodimentis constructed with lateral surfaces 12 which are at right angles to theaxis of the wheel and are of a considerable width. By means of this itis achieved that the width of the gaps l0 and 11 remain more or less thesame, even if the partition 9 is not constructed preciselycircular-cylindrically or is mounted slightly eccentrically. It isconsequently not necessary to meet such exacting requirements as regardstolerance, as farv as the construction and mounting of the ducts isconcerned, as with the embodiment shown in FIG. 1.

It does, moreover, appear from FIG. 4 that the intermediate ring 4 isconstructed with an inside that is constituted of surfaces 13 which aresloping inwards towards the center. A]- ready as a consequence of thesmaller surface area, the deposition of dust is substantially reducedand the use of these sloping surfaces 13 results in an additionalreduction of the risk of dust deposition.

FIG. shows a particularly expedient embodiment of the connection of theblades with the intermediate ring.

In FIG. 5 is seen a blade 14 which is shown according to its normalsection. The blade has this section with essentially the same pitchthroughout, possibly with a outwardly diminishing width of blade,but'within a line in the proximity of the intermediate ring 4 asindicated with the line B in FIG. 4, the section is twisted acutelytowards the plane of the intermediate ring, as seen in FIG. 5. Thereby,on the one hand, a longer connecting surface to the intermediate ring,and on the other hand, a closing of the blade at the end facing theintermediate ring is obtained, such as is obtained in the knownconstruction according to FIG. 1 by means of the intermediate ring, butwhich is impossible to obtain without twisting, when the intermediatering is narrowed.

The axial width of the intermediate ring should be less than half,preferably less than a third of the largest width of the inner vanes asmeasured in an axial direction from their front edges to their rearedges.

The radial width of the intermediate ring should be at least 1% timesthe axial width thereof.

What is claimed is:

l. A double impeller wheel for an axial flow fan comprising a hub;

a set of inner impeller blades each secured at its radially inner end tosaid hub and having an outwardly decreasing axial width;

a connecting ring secured to the radially outer ends of said impellerblades coaxially with said hub; and

a set of outer impeller blades each secured at its radially inner end tosaid ring and having an outwardly decreasing axial width, said inner andouter impeller blades being inclined in opposite directions with respectto the imaxial width of said inner blades. 2. A double impeller wheel asclaimed in claim 1 in which said axial width of said connecting ring issmaller than onethird of the minimum axial width of said inner blades.

3. A double impeller wheel as claimed in claim 2 in which the surface ofsaid connecting ring facing against said hub is composed of twooppositely tapering surface portions each sloping inwardly towards amidplane of said ring perpendicular to the axis thereof.

4. A double impeller wheel as claimed in claim 1 in which the portionsof said inner and outer impeller blades adjacent to said connecting ringare twisted relative to the respective blade profiles remote from saidring so as to merge with said ring at a small angle to a planeperpendicular to the axis of said ring.

5. A double axial flow fan comprising an inner tubular member defining afirst air duct and having a circumferential slot intermediate to itsends;

an outer tubular member surrounding said inner tubular member anddefining therewith an annular second air duct;

an impeller wheel having a hub rotatably supported within said firsttubular member;

a plurality of inner impeller blades secured at their radially innerends to said hub;

a connecting ring secured to the radially outer ends of said innerblades and located in said circumferential slot with its opposed axialend faces spaced from the axial faces of said slot;

the dimension of said connecting ring in the radial direction being morethan 1% times the axial width of said ring between opposed end facesthereof, said axial width being smaller than one-half of the minimumaxial width of said inner blades;

a plurality of outer impeller blades secured at their radially innerends to said ring and extending across said second annular duct, saidinner and outer blades being inclined in opposite directions withrespect to the wheel axis and having outwardly decreasing axial widths,said end faces of said connecting ring being located on opposite sidesof a plane normal to said wheel axis in which the difference between thepressures in said first and second air ducts is substantially zeroduring rotation of said impeller wheel and so close to said normal planethat he differential pressure at each of said axial end faces is smallerthan onehalf of the maximum differential pressure between said ducts.

6. A double axial flow fan as claimed in claim 5 in which said end facesof said connecting ring are located in planes in which the differentialpressure between said inner and outer ducts is smaller than one-third ofthe maximum differential pressure between said ducts.

7. A double axial flow fan as claimed in claim 5 in which the surface ofsaid connecting ring facing against said hub is composed of twooppositely tapering surface portions each sloping inwardly towards amidplane of the ring normal to the axis thereof.

8. A double axial flow fan as claimed in claim 5 in which the portionsof said inner and outer impeller blades adjacent to said connecting ringare twisted relative to the respective blade profiles remote from saidring so as to merge with said ring at a small angle to a planeperpendicular to the axis of said ring.

1. A double impeller wheel for an axial flow fan comprising a hub; a set of inner impeller blades each secured at its radially inner end to said hub and having an outwardly decreasing axial width; a connecting ring secured to the radially outer ends of said impeller blades coaxially with said hub; and a set of outer impeller blades each secured at its radially inner end to said ring and having an outwardly decreasing axial width, said inner and outer impeller blades being inclined in opposite directions with respect to the impeller axis, the dimension of said connecting ring in the radial direction being more than 1 1/2 times the axial width of said ring between opposed end surfaces thereof, said axial width being smaller than one-half of the minimum axial width of said inner blades.
 2. A double impeller wheel as claimed in claim 1 in which said axial width of said connecting ring is smaller than one-third of the minimum axial width of said inner blades.
 3. A double impeller wheel as claimed in claim 2 in which the surface of said connecting ring facing against said hub is composed of two oppositely tapering surface portions each sloping inwardly towards a midplane of said ring perpendicular to the axis thereof.
 4. A double impeller wheel as claimed in claim 1 in which the portions of said inner and outer impeller blades adjacent to said connecting ring are twisted relative to the respective blade profiles remote from said ring so as to merge with said ring at a small angle to a plane perpendicular to the axis of said ring.
 5. A double axial flow fan comprising an inner tubular member defining a first air duct and having a circumferential slot intermediate to its ends; an outer tubular member surrounding said inner tubular member and defining therewith an annular second air duct; an impeller wheel having a hub rotatably supported within said first tubular member; a plurality of inner impeller blades secured at their radially inner ends to said hub; a connecting ring secured to the radially outer ends of said inner blades and located in said circumferential slot with its opposed axial end faces spaced from the axial faces of said slot; the dimension of said connecting ring in the radial direction being more than 1 1/2 times the axial width of said ring between opposed end faces thereof, said axial width being smaller than one-half of the minimum axial width of said inner blades; a plurality of outer impeller blades secured at their radially inner ends to said ring and extending across said second annular duct, said inner and outer blades being inclined in opposite directions with respect to the wheel axis and having outwardly decreasing axial widths, said end faces of said connecting ring being located on opposite sides of a plane normal to said wheel axis in which the difference between the pressures in said first and second air ducts is substantially zero during rotation of said impeller wheel and so close to said normal plane that he differential pressure at each of said axial end faces is smaller than one-half of the maximum differential pressure between said ducts.
 6. A double axial flow fan as claimed in claim 5 in which said end faces of said connecting ring are located in planes in which the differential pressure between said inner and outer ducts is smaller than one-third of the maximum differential pressure between said ducts.
 7. A double axial flow fan as claimed in claim 5 in which the surface of said connecting ring facing against said hub is composed of two oppositely tapering surface portions each sloping inwardly towards a midplane of the ring normal to the axis thereof.
 8. A double axial flow fan as claimed in claim 5 in which the portions of said inner and outer impeller blades adjacent to said connecting ring are twisted relative to the respective blade profiles remote from said ring so as to merge with said ring at a small angle to a plane perpendicular to the axis of Said ring. 